Basic 'AR' Questions ('new' to AR, but not new to UE4)?

I’m trying to get more familiar with AR development in Unreal Engine 4 (I’m pretty familiar with UE4, inc. for VR development).

I realize that 4.19 introduces a unified framework, but I’m trying to find information on AR that instantiates based on specific surfaces / images tracked (rather than a generic horizontal), while retaining ‘world’ information.

Any good resources on where I can dig a little bit into that?

Thank you!